Incidentally, in case it's not clear from Emerson's first message, the
Challenge Grant is not yet running - we're looking for *major* donors
right now to *make* a Challenge Grant. That's why it's called a Challenge
Grant Challenge.

This is the first time SIAI has tried anything like this, so we'll have to
see how it goes. One possible danger, for example, is that all our
ordinary minor donors might start holding off on donations until they see
whether the Challenge Grant starts running (probably a net negative-sum
strategy); or that we'll find enough major donors to run the Challenge
Grant but not enough minor donors to fulfill it.